Pressure sensor

ABSTRACT

A pressure sensor includes a sense element port, a support ring and a plurality of interference fit slits to provide a flexible interference fit between the sense element port and the support ring to form a substantially flush lap joint. The sensor also includes an electronics board inside the support ring and attached to planar mounting tabs which provide a stable mounting. Gel flow barriers protect electronics board features from unwanted non-conductive gel. Double-ended symmetrical, tapered contact springs provide manufacturing cost savings and contribute to improved alignment of an interface connector of the sensor.

FIELD OF THE INVENTION

This invention relates generally to pressure sensors and moreparticularly to sensors using strain gauge technology for sensingpressure change to produce an electrical signal related to such changeand employing electronics for processing and amplifying the signal.

BACKGROUND OF THE INVENTION

Although the use of strain gauge technology for converting changes influid pressure to related electrical signals is known, there exists aneed to provide sensors which are more easily manufactured and whichhave improved reliability and optimum life expectancy. There is also aneed to minimize the cost of producing the sensors so as to make it moreeconomically feasible to use them in given applications and thusincrease manufacturing volume with resulting savings in large volumemanufacturing techniques.

In issued U.S. Pat. No. 6,763,724, assigned to the assignee of thepresent invention, a pressure sensor using strain gauge technology isdisclosed and claimed comprising a tubular port fitting having a fluidreceiving opening at one end and a closed, integrally formed diaphragmat an opposite pedestal end, an angular orientation feature and alocking feature for locking receipt of a support member on the pedestalend. The support member has an aperture flat end wall received over thediaphragm portion, the aperture being in alignment with strain gaugesensor elements glass bonded to the diaphragm portion. Wires are bondedboth to the strain gauge sensor elements and to circuit pads on thebonded lobe section of the flexible circuit assembly and encapsulated bysilicone gel. The entire teachings and contents of this referencedissued patent are hereby incorporated by reference in its entirety.

In automotive applications, the pressure sensors need to be manufacturedin high volume at a low cost and must be very reliable in the harshenvironment in safety critical (e.g., braking system) applications. Inthe assembly of strain gage based pressure and force sensors, theisolation of the sense element diaphragm from mechanical stresses in theelectronics board (due to humidity, thermal expansion, and the like)drives the use of a so-called “support ring”. In existing practice,support rings are made of either metal (soldered to the electronicsboard and butt welded to the sense element port structure) or plastic(glued to the electronics board and snap-fit to the sense element portstructure). The support ring and its attachment should provide a stableplatform for successful wire bonding between the sense element and theelectronics board. Metal support rings also serve as conductive pathsbetween the electronics board decoupling capacitors and the senseelement port structure. In existing practice the support ring is aninternal component of the sensor assembly and is not subject to handlingafter a protective sensor housing is installed around it.

It is important for a consistent weld process that the lip of thesupport ring is uniformly thick, free from burrs, and sits flat againstthe sense element port. In practice, the lip is difficult to form anddefects can result in poor welds due to excessive gaps between supportring and sense element port, burn through of support ring, or a laserwelder missing the support ring to port interface location.

In the assembly of pressure sensors a protective gel as known in the artis dispensed over wire bonds, glass, and gages to protect againstcorrosion (wire bonds) and degradation (glass). Bubbles or voids in thegel, depending on their location, sometimes allow corrosion ordegradation, or cause mechanical damage to bond wires or bonds. Becauseof these problems, it is desirable for the gel to be easily inspectable.Presence of gel (an electrical insulator) on electrical contact springlanding pads can cause unwanted open or intermittent contacts.Typically, wire bond windows in the printed circuit boards (PCBs)through which wires are connected to strain gauges, are generallyrectangular in shape. The assembly is dimensioned such that withtolerance stack-up, it is possible for the edge of the glass nearest theouter diameter of the diaphragm to be obscured by the PCB. The closevertical spacing of the PCB to the diaphragm can lead to a lack of gelflow in this area, leaving the glass (on which the strain gauges aremounted) unprotected from degradation (a cause of output signal offsetshift). There is a need for a design which easily permits gel flow overthe most peripherally located glass. In one conventional solution, gelis prevented from flowing to unwanted locations by a combination ofstrategic placement of SMT components, and by a plastic gel damcomponent. However, there is a need to manage gel flow without use ofadditional components which increase costs, and in some cases requireadditional circuit board real estate, thereby negatively impacting spaceconstraints.

Conventional pressure sensors used in, for example, automotive brakesystems require connections between the pressure sensor and electroniccontrol units (ECU). These connections are often made with springs orspring-loaded pogo pin contacts. Such connections are provided as partof the ECU or as part of the sensor assembly. Conventional pressuresensors typically use relatively expensive pogo pins or springs with oneor two diameters. In some applications the springs are not symmetricaland must be loaded by hand in the assembly process. It is critical toprovide mechanical guidance to the springs to ensure that they makecontact with target pads both inside the sensor and on the ECU. Thesprings must be prevented from buckling. The springs must move freelyalong their axes and provide the required contact forces.

Pogo pin solutions are expensive because they require machined housingsaround the springs and extra sub-assembly operations. Customers do notprefer springs provided as part of the ECU since they require springprocurement, handling, and mechanical guidance. Current solutions withsprings provided as part of the sensor assembly require multi-piecesub-assemblies including printed circuit boards (PCB's) and multipleorientations of the parts or other special measures during assembly (toprevent springs from falling out due to gravity). The solution of insertmolding springs is difficult because of potentially serious difficultieswith methods for properly sealing the mold against the spring,preventing mold flash, and precisely orienting the spring tips towardstheir target contact pads. Furthermore, the cost of handling springs isnot eliminated but merely moved in the supply chain, so no cost benefitaccrues.

SUMMARY

Conventional pressure sensors use expensive contact assemblies, seamwelded components and gel dams to block the flow of protective gel fromcertain area on electronics boards. In contrast to conventional pressuresensor designs, embodiments disclosed herein provide for a singleelectronics board, improved environmental protection, and less expensivecontact assemblies which are easier to manufacture in high volumes.

In one embodiment, a pressure sensor includes a sense element port, asupport ring including at least one mounting tab and a plurality ofinterference fit slits to provide a flexible interference fit betweenthe sense element port and the support ring such that opposing sidewalls of sense element port and the support ring form a substantiallyflush lap joint. The sensor also includes an electronics board disposedinside the support ring and attached to the at least one mounting taband having a plurality of contact pads. Such a design allows parts to bealigned and fit together to provide a much larger process window whenjoining the sense element port and the support ring. This design alsoavoids laser burn through when welding the sense element port to thesupport ring. Special complicated geometry of either the sense elementport or the support ring is not required so the edge condition of thesupport ring is not critical to weld performance and therefore a largerprocess window is provided.

Such a design can provide a sensor without a separate external housingcomponent to save costs. The flexible interference fit providescompatibility with existing laser weld tooling to save capital costs,and is adaptable to resistance welding. The design provides robusthandling because the support ring is exposed in the final assembly. Thedesign does not require selective plating of the support ring whichreduces cost and is compatible with laser thru welding.

In another embodiment, the support ring includes at least three planarmounting tabs, and the electronics board includes attachment padssoldered to corresponding planar mounting tabs and contact padscorresponding to at least three planar mounting tabs. The resultingstable structure avoids flexing the electronics board to preventbreakage of brittle electronic components and provides mechanicalsupport for contact springs in an interface connector.

In yet another embodiment, the electronics board further includes anoversized wire bond window adapted to provide access to sensor contactsto facilitate wire bonding and visibility of the sensor contacts.Changing the conventional rectangular shape of the wire bond windowsolves several problems including the formation of bubbles and voids,inspection of strain gauges and the dispensed protective gel. In aparticular embodiment the oversized wire bond window includes roundedcorners and is lengthened approximately on an axis along a longerdimension of strain gauges mounted on the sense element port. Such adesign facilitates inspection of the strain gauges and the dispensedprotective gel in the wire bond window and reduces problems due toskewing of the window with respect to the strain gauges. Additionally,it has been discovered that such an oversized wire bond shape promotes areduction of bubbles and voids when dispensing protective gel.

In another embodiment, gel flow barriers on the electronics boardinclude a moat to redirect gel flow. The moat includes one or more wallsforming one or more trenches. The moat includes a top layer having anon-wetting surface with respect to a protective gel. By eliminating agel dam to contain unwanted gel, there is one less separate part whichneeds to be attached to the electronics board. In addition toeliminating a component, the opportunity that another part catches onone gel dam is also eliminated.

A technique to form a gel flow barrier includes the steps of:fabricating a plurality of multi-layer trenches and corresponding wallsin electronics printed circuit board (PCB) surrounding a board featureto be protected from a gel flow. The plurality of multi-layer walls formtrenches providing a moat at least partially surrounding a board featureto be protected. Such a technique provides a cost effective mean ofmanaging gel flow and flexibility in the placement of protection fromunwanted gel flow for features on the electronic board. A technique toapply a gel includes providing a gel flow barrier on an electronicsboard the gel flow barrier having a non-wetting surface with respect toa protective gel, positioning the gel flow barrier to protect anelectrical contact pad and providing an oversized wire bond window. Thegel flow is managed by dispensing the gel into the oversized wire bondwindow and over wire bond pads on the electronics board such that thegel flow barrier redirects the gel thereby preventing the gel fromflowing onto the electrical contact pad.

An exemplary interface connector assembly includes an upper spring guideadapted for retaining an elastic contact member and a lower spring guideadapted to attach to the upper spring guide. The elastic contact membercomprises a double-ended symmetrical spring having dual tapered endssuch that a contact point at each end of the spring is closer to acenter axis/center line of the spring. Such an interface connectorassembly provides effective spring capture without the use of expensivepogo pins or PCB's. The connector can be pre-assembled separately, andin some circumstances, the assembly can occur outside of clean-roomconditions required to assemble the strain gauges and spring symmetryreduces orientation concerns during manufacturing and allows forautomated feeding of the springs.

In another embodiment, the springs in the interface connector areconically tapered to further align the spring tip center towards thecenter of a contact receiving pad on the electronics board. A firsttaper effectively causes the spring to have a smaller diameter tip andtherefore reduces locating concerns when aiming for a contact pad of anelectronics board or ECU. Additionally, a second taper allows forreliable capture and retain of the spring in a spring guide.

Such designs and techniques described above facilitate packaging toprovide high volume manufacturing and high reliability. The embodimentsdisclosed herein, may be employed in devices such as those manufacturedby Sensata Technologies, Inc. of Attleboro, Mass., U.S.A.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing will be apparent from the following description ofparticular embodiments disclosed herein, as illustrated in theaccompanying drawings in which like reference characters refer to thesame parts throughout the different views. The drawings are notnecessarily to scale, emphasis instead being placed upon illustratingthe principles disclosed herein.

FIG. 1 illustrates a cross-sectional view of a pressure sensor inaccordance with embodiments disclosed herein;

FIG. 2 is a top plan view of the pressure sensor of FIG. 1;

FIG. 2A is a cross-sectional view taken on line 2A-2A of FIG. 2;

FIG. 3 is a top plan view of an electronics board of the pressure sensorof FIG. 1 including gel flow barriers;

FIG. 4 is a bottom plan view of the electronics board of FIG. 3;

FIG. 5 illustrates a cross-sectional view of the gel flow barrier ofFIG. 3;

FIG. 5A illustrates a top view of the gel flow barrier of FIG. 5;

FIG. 6 is a view of the contact spring of FIG. 1;

FIG. 6A is a side view of the contact spring of FIG. 6 illustrating thespring tip contact; and

FIG. 7 is a view of a contact spring similar to the contact spring ofFIG. 6 having variable pitched active coils.

DETAILED DESCRIPTION

Embodiments of the invention disclosed herein provide for a novelpressure sensor for use in measuring pressure. Embodiments disclosedherein include a newly designed gel flow barrier that isolates certainprinted circuit board (PCB) features and components from protective gelapplied to other areas of the PCB. Additionally, embodiments include anewly designed contact spring adapted to facilitate manufacture of thepressure sensor while minimizing the effect of tolerance stack-up. Inparticular, in one embodiment, a support ring includes planar mountingtabs which provide stable support for a single electronics board andsupport for elastic contact members, for example, double-endedsymmetrical springs having a conical taper at both ends.

FIG. 1 illustrates a pressure sensor 100 configured in accordance withone example embodiment. The pressure sensor 100 includes a contacthousing sub-assembly 108 which includes an upper spring guide 120 (alsoreferred to as upper contact housing) coupled to a lower spring guide134 (also referred to a lower contact housing). The contact housingsub-assembly 108 is coupled to a support ring 110 which is coupled to asense element port 114.

In one embodiment the lower spring guide 134 is coupled to the upperspring guide 120 with a snap fit connection 130. The contact housingsub-assembly 108 includes a plurality of contact springs 118 a-118 n(collectively referred to as contact springs 118 or springs 118) whichare held in place by corresponding spring retainers 116 a-116 n. Thesense element port 114 includes lead-in chamfers 126 and is coupled toport fitting 112. The support ring 110 includes at least oneinterference fit slit 132. The support ring 110 also includes planarmounting tabs 124 a-124 n (collectively referred to as planar mountingtabs 124) to support and electrically contact electronics board 122,also referred to as printed circuit board 122 (PCB) or electronics board122.

In operation, silicon strain gauges 182 (not shown in this view) whichare deposited on a glass surface on a diaphragm produce a signal whichis coupled to the electronics board 122 through wires running routedthrough an oversized wire bond window 140 (FIG. 3) to connections on theelectronics board 122. In response to fluid pressure the diaphragm domesup thereby straining strain gauges 182. The silicon strain gauges 182are wired in a Wheatstone bridge arrangement that is coupled to internalelectronics on the electronics board 122 to provide an offset,conditioned, temperature compensated electronic output reflecting afluid pressure. The electronics board 122 includes a custom integratedcircuit for signal conditioning and other components for filtering andelectro-static discharge (ESD) protection.

Electrical connections between pressure sensor 100 and electroniccontrol units (ECU) (not shown) in, for example, automotive brakesystems, are made with contact springs 118. It is understood that othertypes of elastic contact members can be used in place of springcontacts. The electronics board 122 can optionally convert the outputvoltage to a digital format to communicate with the ECU. The digitaloutput can include redundant signals on a single contact.

During manufacturing the interference fit slits 132 ensure that opposingside walls of sense element port and the support ring form asubstantially flush lap joint contact between the surfaces to be welded.In an alternative embodiment, bump protrusions (not shown) on thesupport ring 110 are designed to mate with a cylindrical portion of thesense element port 114 with a slight interference, self-centering thesupport ring on the port, and ensuring contact between the surfaces tobe welded using, for example, a laser or resistance welding.

In contrast to conventional pressure sensors, the pressure sensor 100support ring 110 does not require protective sensor housing although aprotective housing can be used. In an exemplary sensor, three planarmounting tabs 124 support a single electronics board 122 in contrast tomultiple electronics board used in conventional pressure sensors. In oneembodiment the 100 support ring 110 is a drawn stainless steel part.

In more specific detail, as seen in FIGS. 2 (a top view) and 2A (a crosssection view), pressure sensor 100 includes upper spring guide 120 ofthe contact housing sub-assembly 108 which houses the springs 118. Thesprings terminate in spring tip contact points 162.

The contact housing sub-assembly 108 with springs 118 form the interfaceconnection to the ECU and make electrical connections through the springtip contact points 162. In one embodiment the location of the springs118 and the corresponding planar mounting tabs 124 are designed to meetcustomer ECU specifications, and the contact housing sub-assembly 108 isattached to the support ring via a snap fit. The contact housingsub-assembly 108 also includes snap features 142, access hole 143 andgate for molding upper spring guide 150.

Referring now to FIG. 2A, the support ring 110 includes a plurality ofinterference fit slits 132 to provide a flexible interference fitbetween the sense element port 114 and the support ring 110 such thatopposing side walls of sense element port and the support ring form asubstantially flush lap joint. The interference fit slits 132 and atooling alignment notch provide better manufacturing tolerances and selfcentering and alignment of components during manufacture. In oneembodiment, the flexible interference fit provided by the interferencefit slits 132 minimizes support ring 110 to sense element port 114insertion force and encourages intimate contact between the opposingwalls of the sense element port 114 and the support ring 110. The senseelement port 114 includes the lead-in chamfers 126.

In one exemplary process, the welding laser is aimed at the middle ofthe lap joint 164. In this process, the laser welds through the middleof the lap joint 164 offset from a bottom edge of the support ring 110at approximately at the middle of the substantially flush lap joint,thereby eliminating any support ring bottom edge conditions frominfluencing weld quality and enabling a larger process window than whenusing butt welds. It is understood that the lap joint can be weldedusing a laser (continuous or spot welding), resistance welding or otherwelding techniques know in the art. In certain alternative embodiments,the support ring planar mounting tabs 124 are gold plated to permitsoldering of the electronics board, while the support ring 110 remainsunplated in the region of the weld to prevent contamination of the weld.

Referring again to FIG. 2A, the contact housing sub-assembly 108 (alsoreferred to as spring guide sub-assembly 108) includes the upper springguide 120 adapted for retaining an elastic contact member, here spring118 attached to the lower spring guide 134. In one embodiment, the upperspring guide 120 is snap fitted to the lower spring guide 134, and thespring guide sub-assembly 108 includes three springs. The spring guidesub-assembly 108 including the guided springs 118 provides theelectrical interface connection to the ECU.

Splitting the spring guide sub-assembly 108 into two components allowsfor close guidance of each spring end towards its target, permitscost-effective spring capture without the use of expensive pogo pins orPCB's, and allows the connector to be pre-assembled. The upper and lowerspring guides 120 and 134 are connected to each other by means of snapfit features. The upper and lower spring guides have mating orientationfeatures to ensure proper alignment. In addition to snap fit othertechniques including but not limited to heat staking, welding and gluingcan be used to join the upper and lower spring guides 120 and 134.

Referring now to FIG. 3, the upper side 180 of electronics board 122includes an oversized wire bond window 140, a plurality of gel flowbarriers 172 a-172 n (collectively referred to as gel flow barriers172), a plurality of wire bond pads 174 a-174 n (collectively referredto as wire bond pads 174), a plurality of contact pads 170 a-170 n(collectively referred to as contact pads 170), which are positioned toapproximately align with the corresponding plurality of planar mountingtabs 124 a-124 n. The upper side 180 of electronics board 122 furtherincludes alignment marks 178 a and 178 b (used during wire bonding) anda plurality of PCB test points 176 a-176 n. FIG. 3 also shows straingauges 182 a and 182 b (collectively referred to as strain gauges 182)connected to wire bond pads 174 a-174 n with wires 184 a-184 n. The gelflow barriers 172 on the electronics board 122 include a moat (shown inmore detail in conjunction with FIG. 5) to redirect gel flow.

In one embodiment, the electronics board 122 is coupled to three planarmounting tabs 124 a-124 n. The planar mounting tabs 124 a-124 n define aplane, provide stable support for the electronics board 122 and providemechanical support for springs 118 above them pushing on thecorresponding contact pads 170. This avoids the springs 118 exertingforce on unsupported areas of the electronics board 122. The planarmounting tabs 124 a-124 n also provide attachment points for theelectronics board which can be soldered to the planar mounting tabs 124.The wire bond pads 174 are used for wire bond connections from thestrain gauges 182 (i.e., the Wheatstone bridge) to the electronics board122 and are, in one embodiment, gold plated pads approximately 1/16^(th)inch square. During manufacture of the pressure sensor 100, gel is usedto partially protect wire bond connections from the harsh automotiveenvironment and is dispensed through the oversized wire bond window 140in electronics board 122. In one embodiment, the gel is a two partself-curing flexible gel. The gel is used to cover parts susceptible tocorrosion and to provide a partial environmental seal, but since the gelis non-conductive it needs to be kept away from contact pads 170.

Instead of using several conventional gel flow dams to hold back thegel, the gel flow barriers 172 fabricated on the electronics board 122redirect the flow of the gel around the electronics board 122 featuresto be excluded from the gel flow. In one embodiment, gel is dispensedinto the wire bond window 140 to encapsulate and protect the straingauges 182. The gel continues to be dispensed so that the gel flows outof the wire bond window 140 to cover and protect the wire bond pads 174and wires 184. When the gel reaches the gel flow barrier 172, instead ofholding the gel back, the gel flow barrier 172 redirects the gel flowaround the feature, here contact pads 170, from which the gel is to beexcluded. In this manner, the gel flow barrier 172 prevents excess gelto flow on to areas of the electronics board 122 sensitive to itspresence. Improved gel flow management provides cost savings and qualityimprovement because the use of several additional gel dams is notrequired and the gel flow barriers 172 which are made as part of the PCBmanufacturing process can be flexibly located wherever required on theelectronics board 122. In one embodiment, the gel flow barrier 172 has a“double eyebrow” shape formed from traces in the electronics board 122arranged circumferentially around an electronics board feature to beexcluded from the gel flow, here the spring contact pads 170.

Several other problems exist when dispensing the protective gel.Sometimes the gel doesn't flow where it is directed and occasionally airis trapped forming a bubble or a void in coverage. In these cases, thegel doesn't serve its protective function. Because of these problems itis sometimes necessary to inspect cured gel to see that everything to beprotected has been covered with gel. Furthermore, sometimes theelectronics board 122 is skewed with respect to the strain gauges 182.In response to these problems, it was discovered that changing the shapeof the oversized wire bond window 140 reduces the effects of threeproblems. By providing an oversized wire bond window 140 instead of aconvention rectangular window, it is easier to inspect the gel even ifthe oversized wire bond window 140 is skewed.

In one embodiment, the oversized wire bond window 140 includes roundedcorners and is lengthened approximately on an axis along a longerdimension of strain gauges 182 mounted on the sense element port 114.The oversized wire bond window 140 assures that the edges of the straingauges 182 are not obscured by the electronics board 122 even whenskewed thereby providing for inspection of the strain gauges 182 andwires 184. Another benefit of the oversized wire bond window 140 is thereduced occurrence of bubbles or voids in the protective gel.

Referring now to FIG. 4, the bottom side 190 of electronics board 122includes the oversized wire bond window 140, attachment tabs 196 a-196 cand electrical components 192 a-192 n (e.g., ceramic capacitors) and 194(e.g., ASICS and other ICs). In contrast to conventional designs some ofwhich have cantilevered support for PCBs, the planar mounting tabs 124provide a stable mounting platform. Because the electronics board 122 isattached to the planar mounting tabs 124 which provide mechanicalsupport for springs 118, damage from cracked components 192 and 194 isgreatly reduced.

FIG. 5 illustrates a cross-sectional view of the gel flow barrier 172 ofFIG. 3. The gel flow barrier 172 is made using the printed circuit boardprocess used to fabricate the electronics board 122 and in oneembodiment a base of the gel flow barrier 172 includes a base layer 302,a base copper layer 304, and a pre-impregnated composite fiber layer306. A first wall 320, a second wall 324, a third wall 328 and thecontact pad 170 are disposed on top of the base layer 302. A firsttrench 322 is formed between the first wall 320 and the second wall 324.A second trench 326 is formed between the second wall 324 and the thirdwall 328. A third trench 316 is formed between the third wall 328 andthe contact pad 170. The third trench 316 includes an optional fourthwall 314, here formed by a solder mask layer 336.

The first wall 320 includes a copper layer 308 and the solder mask layer336. The second wall 324, the third wall 328 and the contact pad 170each include a copper layer 308, a copper plating layer 330, a nickelplating layer 332 and a gold plating layer 334. The trenches 322, 326and 316 form a moat which redirects the gel flow before the gel flowreaches the contact pad 170. The top of the moat (i.e., walls 320, 324and 328) is preferably plated with gold because the gel generally doesnot wet to gold which prevents the gel flow from easily crossing thetrenches towards the contact pads 170 which are also gold plated.

In one exemplary manufacturing process, the a gel flow barrier 172 isformed by fabricating the plurality of multi-layer walls 320, 324 and328 and corresponding trenches 322, 326 and 316 in the electronics board122 surrounding a board feature to be protected from a gel flow, forexample contact pad 170 a. The trenches 322, 326 and 316 form a moat atleast partially surrounding the board feature to be protected. Thetrenches can be formed by etching the electronics board down through thecopper layer 308 using PCB board manufacturing techniques known in theart. The top surfaces of the walls 320, 324 and 328 can be plated ortreated with a non-wetting material, for example gold, with respect tothe gel.

Alternative embodiments (not shown) provide a trench to redirect the gelby means of a slot or slots in the PCB through which excess gel candrain downward before reaching the contact pads 170. In anotherembodiment, solder is added to the traces to increase the heights of thewalls. It is also possible to create a dispensed gel flow barrier withoptimize material selection for bead width and height and gel wettingcharacteristics. It is understood that the gel flow barrier 172materials and wall heights and trench width can be optimized forspecific gel types, gel bead widths and heights and gel wettingcharacteristics.

FIG. 5A illustrates a top view of the gel flow barrier 172 of FIG. 5.The gel flow barrier 172 includes the first wall 320, the second wall324, and the third wall 328. The wall form the first trench 322, thesecond trench 326 and the third trench 316. In this embodiment thefourth wall 314 and the first wall 320 enclose the trenches 322, 326 and316.

FIG. 6 shows contact spring 118 of FIG. 1, which is a double-endedsymmetrical spring having a section of active coils 400, first taperedsections 402 (indicated by taper line 408), and ends 404 a and 404 bhaving a section of dead coils which terminate in the spring tip contactpoints 162. The ends 404 have second tapered sections 412 (indicated bytaper line 408). The spring tip contact points 162 make a connection tocontact pads at one end 404 a and to the ECU at the opposite end 404 b.The spring 118 also includes shoulders at the first tapered sections 402which allow the spring 118 to be retained in the upper spring guide 120and lower spring guide 134. Because the spring 118 is symmetrical, handloading into the spring guides 120 and 134 is not required as it is inthe production of some conventional pressure sensors. The double-endedsymmetrical feature facilitates bowl feeding and the use of pick andplace manufacturing equipment. The second tapered sections 412 bring thespring tip contact points 162 closer to a center axis 406 of the spring118. It is understood that the first tapered sections 402 alsocontribute to bringing the spring tip contact points 162 nearer to thecenter axis 406. Springs 118 can be used instead of more costly pogopins or non-symmetrical springs requiring manual assembly, which areboth used in conventional sensors.

Because the target of the spring tip contact points 162 (i.e., contactpads 170) are small and because the assemblies (upper spring guide 120and lower spring guide 134, electronics board 122 and support ring 110)should be aligned to contact three targets at the same time there existthe possibility of tolerance stack up problems. In order to locate theassemblies rotationally and in horizontal dimensions to hit the threetargets, one feature that affects tolerances is a position of thehighest point on the spring (i.e., the spring tip contact points 162).The taper sections 402 and 412 in the spring 118 cause the spring tipcontact point 162 at each end 404 of the spring to be located closer tothe center axis 406 (also referred to as center line 406) of the spring118. In other words, the taper 410 pulls the spring tip contact points162 towards the center, reducing the off center distance of each spring118 and significantly easing the tolerance stack up problem byeffectively providing additional tolerance in the assembly of thepressure sensor 100.

FIG. 6A is a side view of the contact spring of FIG. 6 illustrating thespring tip contact point 162. Because of the taper in spring 118 thespring tip contact point 162 at each end of the spring 118 is closer toa center axis 406 of the spring. In other words, the spring 118 has asmaller diameter tip than the middle of the spring which is beneficialfor contacting the contact pad 170.

FIG. 7 is a view of a contact spring 118′ similar to the spring 118 ofFIG. 6 having a variably pitched active coil portion 400′ includingfirst pitch 416 and here, for example, smaller pitch 418. The variablypitched active coil portion 400′ reduces the incidence of springentanglement due to springs nesting together during automaticmanufacturing operations without affecting the required length and forcespecifications of the contact spring 118′.

Although the invention has been described with regards to specificpreferred embodiments thereof, variations and modifications will becomeapparent to those of ordinary skill in the art. It is therefore, theintent that the appended claims be interpreted as broadly as possible inview of the prior art to include such variations and modifications. Forexample, the invention would equally be applicable topressure/temperature sensors, force sensors, etc.

1. A pressure sensor comprising a sense element port; a support ringincluding at least one mounting tab and a plurality of interference fitslits to provide a flexible interference fit between the sense elementport and the support ring such that opposing side walls of sense elementport and the support ring form a substantially flush lap joint; and anelectronics board disposed inside the support ring and attached to theat least one mounting tab and having a plurality of contact pads.
 2. Thepressure sensor of claim 1, wherein the support ring includes at leastthree planar mounting tabs; and wherein the electronics board includes aplurality of attachment pads soldered to corresponding ones of the atleast three planar mounting tabs and the electronics board includes atleast three contact pads corresponding to at least three planar mountingtabs.
 3. The pressure sensor of claim 1, wherein the sense element portis joined to the support ring by a laser weld offset from a bottom edgeof the support ring.
 4. The pressure sensor of claim 3, wherein thelaser welded lap joint is provided by a spot welding process.
 5. Thepressure sensor of claim 3, wherein the laser welded lap joint islocated approximately at the middle of the substantially flush lapjoint.
 6. The pressure sensor of claim 2, further comprising a pluralityof contact springs mounted along an axis substantially perpendicular tothe corresponding planar mounting tabs and aligned such that the planarmounting tabs provide mechanical support for the plurality of contactsprings.
 7. The pressure sensor of claim 1, wherein the electronicsboard further includes a plurality of gel flow barriers adjacent theplurality of contact pads.
 8. The pressure sensor of claim 1, whereinthe electronics board further includes an oversized wire bond windowadapted to provide access to sensor contacts to facilitate wire bondingand visibility of the sensor contacts.
 9. The pressure sensor of claim8, wherein the oversized wire bond window includes rounded corners andis lengthened approximately on an axis along a longer dimension ofstrain gauges mounted on the sense element port.